Annual blue grass is a cool season weed that should be controlled in fall.
Photo courtesy of NCSU Turffiles
Perhaps you, like me, are looking forward to cooler fall temperatures.
It is has been a very challenging summer, weather-wise, and I’m tired of looking at grey, crunchy grass and sad, wilting plants.
When I compare historical averages from the State Climate office with this year’s weather data collected at the Sandhills Research Station, from February through the present, we had average high temperatures two to four degrees higher compared to the historical average for that month, with the exception of July when the temperature was just slightly above normal.
So far this August it’s six degrees higher than normal, though hopefully forecasted lower temperatures later this week will bring a correction. Rain events have been spotty and overall we’re short two to three inches of rain each month over the historical average, especially for July which is typically our rainiest month. In short, our lawns and gardens are just as hot, tired and thirsty as we are (maybe more).
The upcoming fall would be a good time to give your yard a little extra TLC. In the Sandhills most lawns are warm season grasses: centipedegrass, bermudagrass, zoysiagrass, and St. Augustine. Typically warm season grasses are active as weather warms in spring, then going dormant in the fall as cooler temperatures arrive. “Tender Loving Care” does not mean using a fertilizer containing nitrogen, however.
Take a soil sample. Our soils are naturally quite acidic, and even centipede, the most tolerant of acidic soil of all turfgrass, often needs to have the soil pH raised in order to perform optimally. The North Carolina Department of Agriculture provides free soil tests (exception: the end of November until April 1 it is $4/sample). Material for the tests can be picked up at the Extension office.
Fall is a great time to sample, as you can beat the sample charge and if lime is needed, fall is the best time to apply it. Lime needs between four and six months to modify soil acidity, so a fall application will correct soil pH by the time the grass begins to grow again in the spring.
Not only can the soil report recommendations give you the amount of lime needed to raise the soil pH sufficiently, it can also provide needed levels of other key plant nutrients.
Phosphorus and potassium are two that may need supplementing now. Sandhills soils are naturally low in phosphorus, however if fertilizers containing phosphorus have been used in the past, levels are usually adequate. Once phosphorus is added to the soil, it does not leach readily and is typically present for turfgrass uptake. Low soil pH, however, can bind phosphorus and make it plant unavailable, even if it’s present. The soil report will show the level of phosphorus in the soil and how much, if any, needs to be added. Phosphorus is important for strong root development in turfgrass.
Potassium is another critically important plant nutrient, and typically extremely deficient in Sandhills soils. It leaches readily, so unlike phosphorus, potassium (or Potash) must be added regularly – at least annually. Potassium is important for drought tolerance in plants, and it can also improve cold tolerance. Small pores in plant leaves, called stomata, regulate plant transpiration (the release of water vapor) and intake of carbon dioxide.
This process is directly driven by the presence of potassium ions, so a potassium deficit will negatively impact plant health. Potash, if needed, should be applied four to six weeks before the first frost (which usually occurs around the first week of November in our area).
Another important fall task is managing cool season weeds in the fall and early winter.
Weed problems are often the result of low soil pH and low fertility, however using a preemergent herbicide in October followed up later, if needed, with a postemergent herbicide for small weeds the earlier application missed.
According to Clemson University guidelines, a good rule of thumb is to apply a preemergent herbicide in the fall after 4 consecutive day time temperatures at or below 75 degrees. This is because cool season weed seeds will begin to germinate when soil temperatures drop below 70 degrees. Be sure the herbicide is labeled for the target weed or weeds, and follow label directions.
In late November/early December, scout your lawn for just emerged weeds and if present, plan to use a labeled postemergent herbicide before weeds are taller than four inches, to achieve best control.
It’s been a tough summer. Some work now can help your turfgrass recover over the winter and be healthier by spring green up. For more information on lawn and garden care, contact NC Cooperative Extension, Richmond County Center, at 910-997.8255. Visit our website at Richmond.ces.ncsu.edu and follow us on Facebook